Injection molds are widely used to manufacture plastic parts for different applications, in different shapes. One current application is the molding of relatively thin plastic cards loaded with computer chips, ranging from relatively simple systems used in prepaid long distance phone cards, television cable box identification cards, to cards called xe2x80x9csmart cardsxe2x80x9d including computer software for use with portable computers and the like.
These cards are molded in plastic injection molds, where the cavities of the mold plates are edge filled with plastic material. After filling, a short cooling period transpires. The mold then is opened at a parting line; and movement occurs, facilitating both card and runner ejection. The mold plates carrying the cavities used to form the cards move forward, leaving the runner block of the injection mold machine behind. The runner block is anchored to a fixed mold plate. The action of movement of the mold plates separates the cards from the runners, allowing the runners and cards to be ejected or removed from the mold separately.
The existing design of cold runner plastic injection molds for producing thin, flat computer chip-loaded cards is subject to several shortcomings. The steel components of the cavity blocks on the mold plates and the runner block typically are designed with parallel surfaces, which are perpendicular to the plane of the cards being molded. This results in rubbing (wearing) where the cavity blocks and the runner blocks slide on one another during the opening and closing operation of the mold. This results in wear of one or both of these components, in time. When this wear becomes excessive adjacent the edge of the card being molded, unwanted flash appears on the edge of the card; and production must be stopped in order to repair the mold. It is inherent that this straight design of rubbing steel parts results in steel wear, which requires relatively frequent maintenance. This situation has been tolerated and accepted in conjunction with such molds, even though it results in a significant amount of down time of the mold when parts are repaired or replaced.
Another disadvantage of prior art molds of the type described above, when the runner blocks and the cavity blocks have mating, sliding, parallel surfaces, is that both parts must be manufactured initially with some operating or running clearance. This clearance must be enough to allow the two components to move freely (that is, with a minimal amount of rubbing friction), but not so much as to cause the clearance to be excessive and cause resulting flash on the parts being manufactured. In effect, the running clearance shortens the amount of time that the mold can be run without flash occurring, since such a straight parallel design requires a small amount of wear to be built into the parts at the outset. This built-in clearance necessarily shortens the amount of time the mold can be run before maintenance is required. At the same time, without the initial built-in clearance, excessive wear and stress on the various parts of the mold would occur.
Another disadvantage of prior art molds for manufacturing thin flat, edge filled plastic cards is that the plastic being forced through the gates under high pressure and speed causes the metal in the immediate gate exit to flare out into the edge of the card, where the cutting action occurs to separate the card from the gate. Since the cavity passes by this area, the gate flaring metal begins to wear a corresponding notch in the cavity block, allowing unwanted plastic to flow in the notch. This forms a blemish on the edge of the card formed by the mold. This blemish in turn must be repaired. This occurs when the edge of the card corresponds with the cutting surface of the gate; so that wear in this area results in maintenance being required on the cavity block, as well as on the runner block of the mold.
The above noted disadvantages, inherent in standard or conventional molds for fabricating flat plastic cards with embedded computer chips, cause a significant amount of down time in the use of such molds, as a result of the relatively frequent maintenance intervals which are required in order to repair or replace the various mold parts, including the runner blocks and the cavity blocks. This resultant down time causes increased costs of the cards produced over what would otherwise be possible if the molds could be continuously run with significantly less down time.
It is desirable to provide a design for a plastic injection mold used to fabricate thin, flat plastic card components which overcomes the disadvantages of the prior art noted above, and which eliminates or significantly reduces the sliding metal-to-metal contact between the mold blocks and the runner block of the mold.
It is an object of this invention to provide an improved injection mold design.
It is another object of this invention to provide an improved injection mold design for the manufacture of edge gated cards, with reduced wear on the various mold components.
It is an additional object of this invention to provide an improved edge gated mold design which substantially eliminates rubbing friction between the runner block for the mold and the cavity blocks.
It is a further object of this invention to provide an improved mold design for producing edge gated cards which uses a tapered runner block and tapered surfaces on the cavity blocks to allow metal-to-metal contact during the plastic injection cycle of operation and to permit parting of the various mold parts without sliding metal-to-metal friction to discharge parts from the mold.
In accordance with a preferred embodiment of the invention, a plastic injection mold includes a runner block on a fixed base, with a tapered surface on it. A cavity block is movable relative to the runner block, and has a tapered surface on it for mating with and contacting the tapered surface of the runner block when the cavity block and the runner block are in a plastic injection position. The tapered surfaces of the runner block and the cavity block are designed such that upon relative movement of the cavity block and the runner block, to separate the cavity block from the runner block, the tapered surfaces move away from one another without sliding contact.